Stephen,
I don't know if this is within the purview of Tag, but it would be a handy feature for one of your applications - the ability to determine the ReplayGain information for FLACs one already has. Basically, if wanted to go through my FLAC archive and add replay gain information without re-ripping everything. A google search turned up the following webpage, which might help with this question, but seeing that I know nothing about programming, I can't say for sure:

*UPDATE*
Apparently command line stuff is not as straight forward as I thought it was. While the commands make sense, I cannot for the life of me figure out how to actually run the metaflac program. Any help would be appreciated.